This invention relates to a process for the preparation of acrylonitrile and, more particularly, to a process wherein an antifoulant comprising a polymer of styrene sulfonate is added to at least one step in the quench, the recovery and the wastewater process of an acrylonitrile manufacturing process.
Typically, the manufacture of acrylonitrile comprises three stages, the reaction stage, the recovery stage, and the purification stage. In the reaction stage, propylene undergoes ammoxidation to form acrylonitrile by reaction with ammonia and oxygen. This often is a gas-phase catalytic reaction at an elevated temperature. The resulting acrylonitrile-containing effluent is then quenched with water and unreacted ammonia is neutralized with sulfuric acid. In the recovery stage the quenched product of the reaction stage undergoes a water absorption process to capture acrylonitrile and a recovery process to separate the acrylonitrile from water and other heavy components that also formed during the reaction stage. Water is recycled within the recovery stage. Recovered acrylonitrile is then passed on to the purification stage.
During the recovery stage fouling compounds tend to form and collect in the recycled water. The fouling compounds include both inorganic and organic compounds in the form of monomers, oligomers, prepolymers, and polymers in various combinations. These fouling compounds form deposits along some of the recovery stage equipment such as heat exchangers, reboilers, and columns. When deposited on the heat exchange surfaces of the heat exchangers and reboilers, the fouling compounds reduce the efficiency of heat transfer equipment. Furthermore, the deposition of foulant creates flow resistance through effected equipment, and even causes blockages in the process flow. As a result, periodically the equipment has to be shut down in order to remove the foulant, which results in production loss, cleaning expenditure, operation inconvenience, as well as related safety and environment issues.
Known methods of addressing this problem include adding a dispersant antifoulant to problematic equipment. The dispersant functions as a colloidal stabilizer which keeps foulant suspended in the process stream and prevents foulant from becoming deposited on equipment surfaces. One such example is disclosed in U.S. Pat. No. 3,691,226 which describes the use of lignosulfonate metal salts to minimize foulant deposition on the heat transfer surface of the heater exchangers used to cool recycled water. Another example is U.S. Pat. No. 5,650,072 which teaches the use of naphthalene sulfonate formaldehyde condensate polymer to prevent fouling of heat exchangers in an acrylonitrile stripper.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §. 1.56(a) exists. All patents and patent applications cited within this application are hereby incorporated by reference in their entirety.